1. Field of the Invention
The present invention relates to a light guide device for mixing light of various colors and guiding the mixed light to a display panel, and a back lighting module comprising the light guide device.
2. Discussion of the Background
Recently, information communication devices such as computers, mobile phones and portable information terminals are actively developed. In addition, displays, which have been limitedly used for home appliances such as TVs, expand their applications to a variety of electronic devices such as information communication devices. As one of displays used for these electronic devices, a liquid crystal display (hereinafter, referred to as LCD) has been developed. The LCD includes a back lighting module for illuminating a rear side of an LCD panel so that picture images or information can be clearly recognized by a user.
Generally, the back lighting module includes light sources for emitting three kinds of different colored (red, green and blue: RGB) light, a light guide plate for guiding the light toward an LCD panel, and a plurality of optical sheets for controlling the light oriented from the light guide plate to the LCD panel to improve luminance. In addition, as for the light sources of the back lighting module, light emitting diodes (LED) that are friendly to environments and have a superior light conversion property and a long lifespan.
However, since such a back lighting module is constructed such that different colored light emitted from the LEDs are oriented directly to the LCD panel through the light guide plate, there is a problem in that insufficiently and unevenly mixed light is provided to the LCD panel. Particularly, in a case where it is intended to illuminate the LCD panel by using white light obtained by mixing red, green and blue light with one another, the uneven mixing of light becomes an obstruction to implementation of high-quality white light.
In this regard, there has been proposed a back lighting module including a light mixing plate, which is arranged in parallel with a light guide plate, and a reflecting space having elliptical reflective walls at sides of the light mixing plate. Such a back lighting module is disclosed in International Patent Publication No. WO2002/97324. This back lighting module is configured such that different colored light emitted from a plurality of LEDs is mixed by the light mixing plate and then reflected on the reflective walls in the reflecting space to be transferred to a light guide plate which in turn guides the light toward an LCD panel. However, since the light should pass through the reflecting space where air exists while being transferred from the light mixing plate to the light guide plate in the conventional back lighting module, a light loss increases, resulting in degradation of the transfer efficiency of light and thence considerable degradation of the energy efficiency of the LEDs.